trouble with modify-frame-parameters

[gottlieb]

I execute the following function in *scratch* on a fresh emacs -Q

  (modify-frame-parameters              ; for 2560x1600
   nil '((fullscreen . fullheight) (width . 176) (left . -1300)))

My screen is 2560x1600.  Emacs version is 24.4.  System is gentoo/gnome.

The frame does become fullheight and the width does become 176.
However, left is not correct (it should be flush left but is nearly
centered.
The weird part is if I execute the same command again (a second C-j in
*scratch), the frame moves to the correct, flush left, position.

An explanation would be appreciated.
thanks,
allan

PS If I use the more natural (left . 0) the frame moves near the left
edge but is not flush left (even if executed twice).